Highly permeable carbon nanotubes/polyamide layered membranes for molecular sieving

Abstract Traditional nanofiltration membranes (NFMs) formed by interfacial polymerization (IP) present relatively low water permeance due to the limitation of polymer-based supports. This work reports high-performance carbon nanotubes-polyamide (CNTs-PA) NFMs with interlayer and functional layer covalently coupled. These membranes feature an interpenetrating network structure, which leads to an extremely high Congo red rejection of 99.47%. The water permeance of the optimal membrane (48.98 L m-2h−1 bar−1) is much higher than most membranes with similar Congo red rejection. Meanwhile, the obtained membranes show an excellent selectivity to NaCl/dye mixed solution (the selectivity of NaCl/CR is 150.32). Moreover, this work comprehensively demonstrates the aggregation kinetics of dye molecules under different pH environments, which strongly affects the dye rejection of the CNTs-PA membrane. The membrane exhibits a switchable CR release property that the CR rejection is severely disabled (2.12%) under a strong alkaline environment and immediately re-effective (99.38%) after neutralization. Building on these findings, our work expands the possibilities of NFMs in ultrafast molecular sieving and pH-responsive separation.